The invention relates to a roller bit for rock drilling. In rock drilling, for example for the recovery of petroleum, use is made of roller bits with a bit body which is provided on its upper face with means for coupling to a system of hollow, rotatable tubes, the "drilling string", and on its lower face with a number--often three--of stub axles, with geared cutting elements mounted so as to be freely rotatable about said stub axles, the roller bit being provided between the cutting elements with nozzles which communicate with the axial passage in the drilling string to allow supply of mud.
During operation the roller bit rests with a chosen pressure on the bottom of the borehole and is rotated so that the cutting elements roll over the bottom of the borehole and crush the rock. The mud supplied along the central passage of the drilling string gushes out of the nozzles against the bottom of the borehole so that the debris set free by the drilling head is washed away and taken along in the return stream of mud ascending through the annular space between the drilling string and the borehole wall.
The demands made on the bearings of the cutting elements on their respective stub axles are high, as is clear from the above description of the working of the roller bit. The preferred bearings are those of the "line contact" type, that is cylindrical or taper roller bearings, but so far the use of these has been limited to cylindrical or taper roller bearings of relatively restricted dimensions, so that several of them have been considered necessary for each cutting element. The reason for this is that so far no satisfactory solution for the axial locking and thus the axial load transmission in cylindrical or taper roller bearings in cutting elements of the type in question has been found.